Radio spectrum resources as a kind of valuable natural resources are definite and limited. There is an increasingly conspicuous contradiction between an increasing demand for broadband radio communication and the limited radio spectrum resources along with the development of radio communication technologies. At present the utilization ratio of the spectrum resources can be improved to some extent thanks to the improvement of the technologies, but the demand of system for the spectrum resources still can not be meet. From the perspective of a characteristic of signal propagation, the spectrum resources in lower frequency bands are incomparably superior to those in higher frequency bands. Among the existing spectrum resources, the superior spectrum resources (e.g., the radio communication spectrum resources in the lower frequency bands) have been extensively allocated, thus resulting in very limited spectrum resources that remain; and there is a very low utilization ratio of the allocated spectrum resources, and many of those spectrum resources already allocated to existing radio systems are idle temporally and spatially to some varying extent primarily as a result of the existing spectrum administration and allocation policies where the spectrum resources are allocated in a relatively fixed pattern failing to adapt rapidly to a demand.
In view of this issue, people pay increasing attention to the technologies of Cognitive Radio (CR). The technologies of CR refers to that a cognitive user accesses an incumbent user (i.e. authorized user) frequency band or an CR user (i.e., secondary user or unauthorized user) frequency band opportunistically without posing harmful interference to an incumbent user (i.e., authorized user) or another CR user (i.e., secondary user or unauthorized user) of a spectrum resource, or that a plurality of systems can share a spectrum through a common pool of resources to improve the utilization ratio of the spectrum. The emergence of the technologies of a cognitive radio offer a powerful technical support of addressing the insufficiency of the spectrum resources, performing dynamic management of the spectrums and improving the utilization ratio of the spectrums,
The various of CR technologies have two fundamental features: a cognitive ability and a reconfiguration ability, where the cognitive ability enables CR to capture or perceive information on the use of a relevant spectrum from its operating radio environment to thereby identify a spectrum gap in a specific time domain, frequency domain and space domain and to select an optimum operating frequency band and optimum operating parameters. This process involves three primary steps of spectrum perception, spectrum analysis and spectrum decision. The reconfiguration ability enables a cognitive device to be programmed dynamically in response to a radio environment to thereby allow the cognitive device to transmit data with a variety of radio transmission technologies. Reconfigurable parameters include an operating frequency, a modulation scheme, transmission power, underlying and upper communication protocols, etc.
Taking a blank TV frequency band as an example, an unauthorized radio device can detect a signal of an authorized system below a threshold through an antenna and a receiver using the CR technologies to thereby decide whether a TV channel is being used. Higher The sensitivity required for spectrum perception is typically higher than that required for a receiver of an authorized service. The spectrum perception function is to examine every frequency band and find those available frequency bands (i.e., spectrum gaps) with the strength of a detected signal below a threshold. Unlike a general receiver, it is only necessary for spectrum perception to judge whether there is a signal present in a specific frequency band without decoding the received signal.
In view of the foregoing introduction of the prior art, the broadcast frequency band with a low utilization ratio can have an idle spectrum used for a mobile communication system to thereby improve the efficiency and coverage of the mobile communication system if the mobile communication system share the 700 MHz frequency band with a broadcast system with the CR technologies. However in order to ensure no influence on normal operation of the broadcast system, a technology compatible with an existing system and provided with a cognitive function has to be designed to thereby perform the CR function in the mobile communication system using the spectrum perception and spectrum obviation technologies.
However an existing mobile communication system, e.g., a Long Term Evolution (LTE) system, is designed for a pre-deployed stable authorized frequency band without taking into account various demands when an operating frequency band of the system is a cognitive, instable and unauthorized frequency band. Thus no appropriate solution has been designed for such a scenario that when the mobile communication system is deployed at a cognitive frequency band (unauthorized frequency band), it shall be ensured, as needed, as much as possible that no influence will be posed on communication of an incumbent user, where the mobile communication system shall quit rapidly the cognitive frequency band and select a new frequency band for establishing a cell upon detection of the occurring of an incumbent user, and in this process, the user shall be further handed over to the newly established cell to thereby ensure service continuity of the user. Thus the performance indexes required for the CR technologies can not be accommodated if the mobile communication system and the user equipment deployed in the cognitive frequency band operate purely as in the existing design solution.